SQL query to calculate totals from table that has overlapping/duplicate data - sql

Question

I need to calculate the total number of items from a table that has smaller building units. For example, let's say I have
Unit_Table
UnitId StartUnit EndUnit QtyUnit
---------------------------------------
1 0 2 5
1 0 15 20
1 2 15 15
1 15 30 8
2 0 2 2
2 0 15 12
And let's say I have
Final_Table
UnitId StartFinal EndFinal QtyFinal
----------------------------------------
1 0 30
1 0 15
1 2 30
2 0 15
How do I populate the QtyFinal column with the correct numbers (28, 20, 23 and 12 in this example)? Let's assume that all building blocks necessary for Final_Table are in Unit_Table
The following query does not work:
;With Aggr As (
Select F.UnitId
, F.StartFinal
, F.EndFinal
, Sum(U.QtyUnit) As QtySum
From Final_Table As F
Inner Join Unit_Table As U
On F.UnitId = U.UnitId
Where F.StartFinal <= U.StartUnit
And F.EndFinal > U.StartUnit
Group By F.UnitId
, F.StartFinal
, F.EndFinal
)
Update Final_Table
Set QtyFinal = QtySum
From Final_Table As F
Inner Join Aggr
On F.UnitId = Aggr.UnitId
And F.StartFinal = Aggr.StartFinal
And F.EndFinal = Aggr.EndFinal
The problem is that the Unit_Table has overlaps ((0-2) (2-15) and (0-15) for UnitId 1, for example), how do I eliminate rows 0-2 and 2-15 from the aggregate function for calculating 0-30?

Answer 1

I was thinking about processing Final_Table first. Then, for each row, we can look "the path" from Start to the End in the Unit_Table.
DECLARE
VarStart NUMBER;
VarEnd NUMBER;
VarQty NUMBER;
TotalQty NUMBER;
BEGIN
FOR i IN (SELECT * FROM Final_Table ORDER BY 1, 2) LOOP
VarStart := i.StartFinal;
VarQty := 0;
TotalQty := 0;
LOOP
SELECT EndUnit, QtyUnit
INTO VarEnd, VarQty
FROM Unit_Table
WHERE UnitID = i.Unitid
AND StartUnit = VarStart
AND ROWNUM = 1;
TotalQty := TotalQty + VarQty;
VarStart := VarEnd;
EXIT WHEN VarEnd = i.Endfinal;
END LOOP;
UPDATE Final_Table
SET QtyFinal = TotalQty
WHERE UnitId = i.Unitid
AND StartFinal = i.Startfinal
AND EndFinal = i.EndFinal;
END LOOP;
END;
/
I tried it and the result is:
UNITID STARTFINAL ENDFINAL QTYFINAL
1 0 15 20
1 0 30 28
1 2 30 23
2 0 15 12
Of course, there's a problem when "the path" its not completed in Unit_Table, like this:
UnitId StartUnit EndUnit QtyUnit
---------------------------------------
3 0 2 7
3 15 30 11
... But I don't know if it is possible in your application. Maybe this can't happend because is one of your requirement before inserting in Unit_Table.

Answer 2

I think you need a correlated subquery or cross apply:
Update F
Set QtyFinal = u.QtyUnit
From Final_Table F cross apply
(select sum(u.QtyUnit)
from Unit_Table u
where F.UnitId = u.UnitId and
F.StartFinal <= u.StartUnit And F.EndFinal > u.StartUnit
) u;
Notes:
The update needs the table alias defined in the from clause. Otherwise, it is a different reference to the table.
If you are not familiar with cross apply, it is a lot like a correlated subquery in the from clause.
A correlated subquery would be similar, but it would update all rows instead of only those that match.